The present invention relates to circuits for shutting off a sensor controlled switch coupled between an AC line and an AC load.
Automatic, sensor-controlled switches are often used for certain AC loads, such as lights. These sensors might detect sound or motion in a room to turn on or off lights, for instance. Such a sensor circuit couples to the AC line and derives its power from the AC line voltage. One such sensor controlled switching circuit is shown in U.S. Pat. No. 4,820,938.
It is desirable to have a manually operated switch which will turn off such a sensor circuit. UL requirements call for such a switch to shut off current completely to the circuit, and not maintain a low current for monitoring when it is off. In addition, UL requirements require that the device be able to shut off in the event that there is an open circuit in the AC line, such as by a light burning out. Typically, these requirements have been met with a high current transformer switch which is bulky and expensive. This high current switch is in addition to a switch which is used by the sensor during its normal operation. Thus, two switches are needed for the circuit.